This invention relates generally to a method and apparatus for reducing residual gases from a foamed polymer material, and particularly comprises a method and apparatus for accelerating the diffusion of isobutane gas from foamed plastic material.
There has been a proliferation of the introduction of foamed polymer products into the marketplace including the manufacture and sale of extruded tubes for insulation, foamed rods, water toys commonly referred to as xe2x80x9cnoodlesxe2x80x9d and foams for packaging and paddings and upholstery material. Generally speaking such products are extruded through an extruder die. In particular the foamed polymer can comprise of a variety of substances including polyethylene or the like. A foaming agent is generally included with the polymer material in order to cause the extruded part to expand as it leaves the extruder die to a preselected size.
A variety of foaming materials can be used, the most common of which includes isobutane gas that is mixed with the thermo plastic material such as polyethylene so as to produce a foamed thermo plastic extruded profile as it exits through the extruder die. The isobutane gas is introduced to cause the material to foam or expand outwardly to produce the excellent insulating qualities of the insulating tube as well as the high buoyancy of the water toys referred to above.
Isobutane gas is used because of its inexpensive nature as well as versatility in the manufacturing process. However, the isobutane gas is highly volatile and explosive if subjected to a spark or fire and accordingly such foamed thermo plastic materials are generally warehoused for approximately 10 days or more.
During these 10 days or more the isobutane gas diffuses outwardly and dissipates from the foamed thermo plastic material while atmospheric gases diffuse back into the thermo plastic material to replace the isobutane gas which has left. Accordingly manufacturers of foamed thermo plastic materials utilizing volatile organic compounds such as isobutane must generally include large warehousing facilities to xe2x80x9cagexe2x80x9d the foamed thermo plastic material so as to reduce the possibility of explosions during transport of the foamed thermo plastic materials to the distributors and ultimate users. After the 10 days there is still some residual isobutane gas contained within the product but it is at a much lower level.
Therefore generally speaking the industry has warehoused the foamed thermo plastic materials for approximately 10 days or more before shipping same. The foamed thermo plastic materials can be shipped in ventilated transport trucks so as to further ventilate the diffusion of isobutane gas from the foamed thermo plastic materials. There have been a number of instances in the marketplace where transport trucks have exploded due to accidental introduction of spark or flame since isobutane gas is generally heavier than air and may explode if a truck driver stops to light a cigarette or the like.
Manufacturers in the industry have attempted to control the diffusion of the volatile organic compound such as isobutane or the like through the use of additives such as glycerol monsterate an hydrogenated vegetable oil or the like. The use of such diffusion control agents are carefully controlled since too much or too little of the diffusion control agent can cause wrinkling in the surface of the foamed thermo plastic material as well as shrinkage in the cross-section of the thermo plastic foam material.
Accordingly there is a need for an improved method of accelerating the diffusion of residual gases such as isobutane or the like.
Various attempts have heretofore been made in the prior art to evacuate gasses from an extrusion process. For example, U.S. Pat. No. 5,306,132 teaches a process and a degassing unit for the degassing of plastic melt in a screw extruder in which a surface of the degassing unit facing the screws of the extruder are heated to prevent deposition of entrained plastic particles, particularly at the corners or edges of the degassing unit. Prior to the commencement of the treatment process, the degassing unit is heated to a temperature which is at least as high as the melting point of the plastic to be treated. Heating can be effected by conveying a heating medium through a channel in the degassing unit located in proximity to the surface facing the extrusion screws and especially the corner or edge regions.
U.S. Pat. No. 5,287,634 teaches removal of vaporizable components from polymeric products. More particularly, undesirable vaporizable components are removed from biomedical polymeric products. Heated nitrogen gas is supplied to an evenly distributed within and around a heated chamber having biomedical polymeric products contained therein. The heated gas is introduced into the chamber through omnidirectional multi-point source dispersion means. The products are rotated about an axis to further evenly distribute the heated gas over the surface of the product. The heated gas vaporizes vaporizable components and carries them to a collection area where the vaporizable components are deposited.
U.S. Pat. No. 4,298,322 teaches venting means for a screw extruder, particularly for thermo-plastics material, which venting means comprises a substantially vertical venting shaft communicating with the bore of a cylinder of the extruder and coupled to a low pressure source by a pipe, a pivotable flap which is moved from its normal position shown, when acted upon by plastics melt being extruded and rising in the shaft due to malfunction of the extruder, to cover the end of the pipe and prevent the melt passing into the pipe.
U.S. Pat. No. 3,325,640 teaches a method of processing a plastic material comprising the steps of maintaining a vacuum in said working space, whereby positively to expel from out of the material and draw out of the working space any gaseous and volatile inclusions present in the material as such inclusions are presented to said exposed boundary surface.
U.S. Pat. No. 2,697,255 teaches a process for removing by diffusion through the walls of the closed cells a major portion of the gas from the gas-containing cells of a cellular thermoplastic body thereby contracting the thermoplastic body and increasing the specific gravity thereof thus forming a stable thermoplastic body. A process of dimensionally stabilizing and increasing the specific gravity of expanded, gas-containing, closed-cell, cellular bodies of natural and synthetic elastomers and thermoplastic resins, comprising the steps of slicing a completely expanded, closed cell, gas-containing cellular body into thin slices of the same; heating said thin slices to a temperature above the heat distortion temperature and below the softening point of said cellular body until a portion of the gas contained in the closed cells of said cellular body diffuses into the surrounding atmosphere, thereby decreasing the gas content of said closed cells and causing said cellular body to contract, thus forming a dimensionally stable closed-cell, cellular body having the specific gravity thereof increased in comparison with the specific gravity of the original cellular body.
It is also an object of this invention to provide a method of reducing the warehousing time in the xe2x80x9cagingxe2x80x9d foamed thermo plastic materials from approximately 10 days down to two days.
It is also an object of this invention to provide an improved method and apparatus for improving the safe transport of the foamed thermo plastic materials.
It is also an object of this invention to provide an improved method and apparatus for the capture and reclaim or destruction of these residual gases.
These and other objects and features of the invention shall now be described in relation to the following drawings.
It is an aspect of this invention to provide a method of reducing residual gases from a foamed polymer material by subjecting said foamed polymer material to a vacuum.
In accordance with yet another aspect of the invention, to provide a method of accelerating the diffusion of volatile isobutane gas from a foamed extruded product comprising extruding a thermo plastic material with isobutane gas so as to produce said foamed thermo plastic material; placing said foamed thermo plastic material in a vacuum chamber; subjecting said foamed thermo plastic material to a vacuum for a time duration of between 10 and 20 minutes at a vacuum of about 28 inches mercury so as to accelerate the diffusion of isobutane gas; then drawing said isobutane gas from said vacuum chamber.
It is a further aspect of this invention to provide an apparatus for reducing residual gases from foamed polymer materials using a vacuum chamber.